I did a 30 overbore on mine as well, it’s worked out great. No issues with thin cylinder walls, overheating or any of that (which is a danger if you would go with a 60 overbore, I have heard). One thing I did prior to putting mine together was to “JetHot coat” my piston tops. It only cost about $200 and with the heat the turbo produces, we (the expert that helped me build my engine) thought it’d be a good idea. I read a lot about it at the time, and it seemed like a smart move, especially since the only pistons I could get that weren’t a million dollars were cast and not forged. Also, my particular engine (pre-rebuild)had a piston (#8) which had shattered its skirt and thrown a piece of it through the block. I figured the JetHot coating was cheap insurance…I can look up the company info if you’re interested. They turned it around real quick (like a week if I remember right).